This invention relates in particular to devices for dynamometer testing of motor vehicles, that is, devices which are adapted to be connected to a driven vehicle output shaft and which include means for measuring one or more quantities significant to the performance of the engine and the transmission, such as the torque that the driven shaft applies to a power-absorbing device forming part of the test device.
One such device is disclosed in EP 0 210 979, which discloses a device including power-absorbing means in the form of a hydraulic pump assembly which has an input shaft adapted to be in engagement with a driven vehicle shaft using a rigid coupling. The pump assembly consists of two pumps, which are drivingly interconnected and thereby both driven by the shaft. An adjustable control valve is controlled such that the valve allows the passage of a liquid flow, the volumetric rate of which being related to the desired rotational speed of the rotor, i.e. of the driven vehicle shaft. By controlling the working pressure of the pumps, a desired torque can be applied to the drive shaft of the vehicle, and, thereby, the performance of the engine can be tested.
A problem with this device, however, is that as vehicle engines increasingly tend to generate higher and higher powers, and higher and higher torques, the heat generated by the power-absorbing means when testing these engines, e.g., as a temperature rise of the hydraulic fluid when passing through the control valve, becomes more difficult to cool.